A standard thermostatically regulated valve such as described in German patent 3,530,812 filed Aug. 29, 1985 by J. Kostorz has hot- and cold-water inlets connected to respective valve seats whose other sides open into an outlet compartment from which tempered water flows. A double valve body is displaceable in one direction to increase the flow from one of the inlets to the outlet compartment and decrease the flow from the other compartments and is oppositely movable for the opposite effect. This valve body can be moved by axially displacing an externally displaceable stem, and is also provided with a temperature-sensitive element in the outlet compartment that can change length to move the valve element and keep it at the setting it is originally put into. Thus once a given mixed-water temperature is set, the temperature-sensitive element will automatically move the valve bodies in response, for instance, to varying supply temperatures to keep the output temperature steady.
The manual setting of such a valve is typically by means of a simple knob mounted on the rotatable and axially displaceable valve stem. In addition in order to prevent the user from accidentally scalding himself or herself, it is standard to provide abutments which limit the angular travel of the knob so that it cannot be turned too far in the hot direction past a predetermined maximum safe temperature. Some means is also provided, typically in the form of a depressible latch button, to eliminate this safety feature. Such an arrangement is disadvantageous in that the safe temperature cannot be changed readily. In addition the knob moves axially with the stem so it is not possible to provide an accurately readable scale indicating the set temperature.
In another system known from German patent document 1,161,460 filed Sep. 27, 1962 by W. Gruber a scale is provided that is fixed on the valve housing and that indicates the maximum safe temperature the valve is set to. A button can be depressed to change this temperature and establish a new range of adjustment for the valve. Such an arrangement cannot, however, be used on a valve where the stem moves axially when it is rotated.